1. Field of the Invention
The present invention relates generally to image processing and, more specifically, to feature matching in distorted images.
2. Description of the Related Art
Images often include features, or regions of an image that have some property that makes a region of the image noteworthy for certain purposes. The features may be edges, curves, points, two-dimensional shapes, or other regions, and the features typically arise from the scene depicted in the image. Depending on what is depicted in the image, the features may be features arising from the depiction of objects in the image, for example corners of furniture, edges of walls, facial features of people, or other visible items, or in other examples, the features may arise from phenomena created by such objects, for example shadows, glare, lights, and the like.
Images often have features that are machine recognizable. For example, a tennis racket appearing in an image may produce a number of features, such as edges of the handle, edges of the strings, a shadow from the racket on a table, and a glare from the racket, and an image-processing machine, such as a properly programmed computer, may detect those features. The detected features may be used for a number of purposes. For instance, the image-processing machine may be configured to identify objects appearing in images based on correlations between the features identified in the image and features stored in memory associated with other images of a given item. In another example, the image-processing machine may be configured to match features appearing in two different images and align the two different images with one another based on the matched features or examine differences between the appearance of the same feature in two different images, e.g., to identify attributes of the environment in which the two images were captured, such as differences in camera position or differences in the behavior of light passing through different regions of a camera lens.
Matching features between images that are distorted is often difficult. For instance, spatial distortion often changes the spacing between, and relative size of, the features of the same object appearing in differently distorted portions of images, e.g., based on where the features appear within an image. For instance, features appearing near a left edge of an image may be distorted such that the features are reduced in size in the image and appear smaller relative to features near the center of the image that are, in the scene being imaged, the same size. Distorting the relative size and spacing of the features within an image, particularly when the distortion is based on where those features appear within an image, often impedes efforts to match similar features appearing in other images in which the features are not distorted or other images in which the features are distorted in a different way, e.g., in a different portion of another distorted image.